1. Field of the Invention
The present invention relates to an organic electroluminescence device (hereinafter also referred to as “organic EL device”) capable of emitting light by converting electric energy to light.
2. Description of the Related Art
Since organic electroluminescence devices (organic EL devices) are capable of obtaining emission of light of high luminance by low voltage driving, they are actively researched and developed. An organic EL device generally comprises a pair of electrodes and an organic layer between the pair of electrodes, electrons injected from the cathode and holes injected from the anode are recombined in the organic layer, and generated energy of exciton is used for emission of light.
In recent years, increment in efficiency of devices has been advanced by the use of phosphorescent materials. As the phosphorescent materials, iridium complexes and platinum complexes are described in U.S. Pat. No. 6,303,238. However, devices that satisfy compatibility of high efficiency and high durability are not yet developed.
For the intention of obtaining materials of high durability, organic EL devices using a compound having an electron-defective nitrogen-containing heterocyclic group as the material are described in JP-A-2003-138251, JP-A-2004-103463 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.) and Chemistry of Materials, Vol. 10, pp. 3620-3625 (1998).